1. Field of the Invention
The present invention relates to an ink jet printing apparatus and an ink jet printing method to form an image on a print medium using a print head that has a plurality of ink ejection openings.
2. Description of the Related Art
In an ink jet printing apparatus that forms an image on a print medium by ejecting ink droplets, a print head is used that has a plurality of fine ink ejection openings and liquid paths communicating to the openings (a combination of each ink ejection opening and its associated liquid path is also called a “nozzle”). When a bubble is present in a nozzle or liquid path of such a print head, an ink ejection performance of the print head may deteriorate. More specifically, the presence of a bubble may result in an ink droplet failing to be ejected from the print head or an ejected ink droplet deflecting from an intended direction, causing a landing position error. A bubble may be produced in the print head when external air enters from an ink ejection opening into a liquid path filled with ink or when it enters into a tube filled with ink and further into the print head. Also in a print head that ejects ink by an expanding force of a generated bubble, there is also a possibility that minute air residues may accumulate to form a bubble in the nozzle.
To avoid such an ink ejection performance degradation due to air present in the print head, a recovery operation to clear the nozzles and liquid paths of residual air by refreshing ink in the nozzles has been performed.
One such recovery operation uses a cap capable of covering an ejection opening formation face of the print head and a pump connected to the cap. This operation involves covering the ejection opening formation face with the cap and introducing a negative pressure produced by the pump into the cap to forcibly suck out ink from the nozzles of the print head into the cap. This recovery operation is also called a “suction-based recovery operation”. Other recovery operations include a preliminary ejection operation which ejects ink not contributing to image printing from the ejection openings of the print head, and a wiping operation that wipes the ejection opening formation face. These recovery operations, such as suction-based recovery operation, preliminary ejection operation and wiping operation, are executed in combination.
Of the air present in the nozzles of the print head, air that has entered from the ejection openings into the liquid paths and air that has entered into a tube may increase in volume over time. Generally, the above recovery operation is performed at predetermined intervals to prevent the degradation in the ejection performance of the print head caused by the trapped air. A control to execute the recovery operation at predetermined intervals is also called an “automated timer recovery control”.
This automated timer recovery control, however, has the following problem. Since the recovery operation is performed at predetermined intervals, a certain amount of ink is discharged every time the recovery operation is performed. This in turn increases a running cost and makes it necessary to increase a waste ink tank for collecting the discharged ink.
The amount of air trapped in the liquid paths and tube varies depending not only on the elapse of time but also on the environment and condition in which the printing apparatus is used. That is, the interval between the recovery operations varies according to the environment and condition of use of the printing apparatus. In the automated timer recovery control, however, the recovery operation is set to be executed at relatively short intervals to ensure that the recovery operation is initiated early to reliably prevent the ejection performance degradations. So, the recovery operation is performed more than necessary, which in turn increases the volume of ink consumed by the recovery operations. Reducing the volume of waste ink that is discarded more than necessary is now a grave issue in terms of the running cost. Particularly, for a user who prints an image only rarely, since the volume of ink actually used for printing is not so large, a ratio of the ink volume discarded by the recovery operation to the total ink consumption becomes high. For such a user, the running cost is even higher.
Japanese Patent Laid-Open No. 2003-182052 proposes a construction that enables a user to choose between an execution of a recovery operation by the automated timer recovery control and a prohibition of execution. Japanese Patent Laid-Open No. 2005-335238 proposes a construction that controls the interval between recovery operations according to the state of printing.
However, the ink jet printing apparatus described in the Japanese Patent Laid-Open No. 2003-182052 simply allows the user to choose between the execution of recovery operation based on the automated timer recovery control and the prohibition of execution. So, once the user selects the prohibition of execution, the recovery operation based on the automated timer recovery control is not executed until the prohibition is reset. In that case, although the ink volume discarded by the recovery operation can be reduced substantially, the print head's ejection performance will likely deteriorate because no recovery operation is executed. When the ejection performance of the print head deteriorates, a quality of printed image will also deteriorate.
In the ink jet printing apparatus described in Japanese Patent Laid Open No. 2005-335238,the interval at which to perform the recovery operation is controlled by the automated timer recovery control according to the printing state, such as the kind of an image being printed and the time that has elapsed from the previous printing operation. If the interval of the recovery operation is set long by this control, the timing of execution is delayed from when the recovery operation is normally executed by the automated timer recovery control. The ejection performance of the print head during the delay period of execution timing is presumed to be maintained at a proper level in a general condition of use. However, depending on the condition of use of the printing apparatus by the user, the ejection performance of the print head may deteriorate. Therefore, it is difficult to perfectly guarantee the ejection performance of the print head depending on the environment of use of the printing apparatus and the printing state.